Subclass of `AsyncFileSystem` doesn't use its `_walk`, goes straight to `AbstractFileSystem.walk` instead

[dAnjou]

Hi, me again, and apologies if I've missed something again.

As the title says, the following code shows that when I call ls on a subclass of AsyncFileSystem it goes to the async version _ls and raises, as expected:

from fsspec.asyn import AsyncFileSystem


class FooFS(AsyncFileSystem):
    pass


if __name__ == "__main__":
    foo_fs = FooFS()
    foo_fs.ls("foo")
    for x in foo_fs.walk("foo", on_error="raise"):
        print(x)

Traceback (most recent call last):
  File "/tmp/foo/test.py", line 10, in <module>
    foo_fs.ls("foo")
    ~~~~~~~~~^^^^^^^
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 118, in wrapper
    return sync(self.loop, func, *args, **kwargs)
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 103, in sync
    raise return_result
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 56, in _runner
    result[0] = await coro
                ^^^^^^^^^^
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 709, in _ls
    raise NotImplementedError
NotImplementedError

However, if I let it call walk then it goes to AbstractFileSystem.walk (which itself then calls the async'ed ls) instead of AsyncFileSystem._walk:

from fsspec.asyn import AsyncFileSystem


class FooFS(AsyncFileSystem):
    pass


if __name__ == "__main__":
    foo_fs = FooFS()
    # foo_fs.ls("foo")
    for x in foo_fs.walk("foo", on_error="raise"):
        print(x)

Traceback (most recent call last):
  File "/tmp/foo/test.py", line 11, in <module>
    for x in foo_fs.walk("foo", on_error="raise"):
             ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/spec.py", line 432, in walk
    listing = self.ls(path, detail=True, **kwargs)
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 118, in wrapper
    return sync(self.loop, func, *args, **kwargs)
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 103, in sync
    raise return_result
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 56, in _runner
    result[0] = await coro
                ^^^^^^^^^^
  File "/tmp/foo/.venv/lib64/python3.13/site-packages/fsspec/asyn.py", line 709, in _ls
    raise NotImplementedError
NotImplementedError

Is there something I should do for it to use the async walk?
🙏